Abstract
We studied the abundance of calanoid copepods of the genus Calanus in a high-resolution sampling grid located in the vicinity of a breeding colony of an avian Calanus predator, the little auk (Alle alle) in an Arctic fjord (Isfjorden, Svalbard) in July 2007. Within diving reach of little auks, all copepodite stages of C. finmarchicus, as well as stages CIII–CV of C. glacialis, were recorded in all 26 stations sampled. Spatial autocorrelation analysis was used to detect spatial heterogeneity (patches) in the distribution of Calanus spp. Positive spatial autocorrelation was detected on scales up to 1.2 km for C. finmarchicus stages CIII–CV and for C. glacialis CIV and CV, but was rarely detected for the younger stages. This suggests that the tendency to form patches varies with ontogeny in Calanus spp. At an adjacent little auk colony, the diet prey composition from 30 gular pouches of little auks returning from feeding trips was investigated. Calanus glacialis CIV and CV were numerically dominant in the prey samples, while C. finmarchicus CIV which was dominant in the net samples did not contribute to the little auk diet. This could suggest selective feeding, a detection of patches beyond the scale of our survey, feeding beyond the sampling area or a combination of these factors. Large Calanus abundance differences within the sampling grid underline the necessity of a proper choice of grid size, in this case 2 km between stations.
Highlights
IntroductionCharacteristic horizontal length scales of plankton patches range from less than 1 m to more than 104 m (Legendre et al 1986; Tsuda et al 1993; Currie et al.1998; Mann & Lazier 2006, see Table I for details)
Spatial heterogeneity of marine zooplankton can be substantial (Hardy 1936; Mann & Lazier 2006).Characteristic horizontal length scales of plankton patches range from less than 1 m to more than 104 m (Legendre et al 1986; Tsuda et al 1993; Currie et al.1998; Mann & Lazier 2006, see Table I for details).Such variability can complicate interpretations of ecological data sets obtained from a limited number of sampling stations as such data may not adequately capture relevant meso- and fine-scale spatial variability (Hembre & Megard 2003)
Calanus glacialis CIV and CV were numerically dominant in the prey samples, while C. finmarchicus CIV which was dominant in the net samples did not contribute to the little auk diet
Summary
Characteristic horizontal length scales of plankton patches range from less than 1 m to more than 104 m (Legendre et al 1986; Tsuda et al 1993; Currie et al.1998; Mann & Lazier 2006, see Table I for details) Such variability can complicate interpretations of ecological data sets obtained from a limited number of sampling stations as such data may not adequately capture relevant meso- and fine-scale spatial variability (Hembre & Megard 2003). Ecological studies often extrapolate data based on only a few sampling locations that at best reflect variability on one or a restricted number of spatial scales Such investigations may produce over-smoothed data sets that render the detection of ecologically significant variability unlikely and may potentially lead to biased interpretations (Young et al 2009). It is of importance to design the sampling scheme in a way that captures the variability relevant to the processes of interest
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